GPS - some terminology!

For my first post, I will share some information about GPS - Global Positioning System. I will delve one step deeper than a basic explanation of how a GPS system works and introduce some terminology.

GPS, like we all know is the system useful for identifying one's position, velocity, & time using signals from satellites (referred to as SV or space vehicle in literature). It uses the principle of trilateration (not triangulation which is misused frequently) for locating.

The dumbed-down version of GPS involves a receiver searching for satellites and acquiring its signals. It then starts to track and decodes the satellite's information. Satellites also transmit information about the entire constellation. By decoding the messages from the satellites, a receiver computes its distance from the satellites. After getting the distance from at least 4 Satellites, it solves a system of non-linear equations (distance formula) to identify its own co-ordinates. I will introduce the jargon involved in the above process with an easy to remember analogy.

Imagine you walk into a party. You look around and scan for people you know. After realizing you don't know anyone, you scan for somebody to talk to. You start a friendly banter and end-up becoming friends with a person. Then you get your friend's mobile number. After spending some more time, you get to know your friend's friends and get their numbers (so that you know where everyone else in case you are not able to contact directly).

Now, the same story in our context -

Imagine you walk into a bar

You scan for somebody to talk to -> Acquisition

You start a friendly banter and end-up becoming friends with a person -> Tracking

You get your friend's mobile number -> Ephemeris

You get to know your friend's friends and get their numbers -> Almanac

And with all this new-found-friends, you will never be lost!

Cheers,

Vivek

P.S. : For my next post, I will talk about the concept of time in GPS. I spent quite some time to understand the relevance of absolute time and relative time-difference in the context of GPS and I will share my understanding. Please feel free to suggest or comment or correct!